The conformity rule requires that Federal, State, and local transportation and air quality agencies establish formal procedures to ensure interagency coordination on critical issues.
Conformity determinations must be made at least every four years, but may occur more often if metropolitan transportation plans or TIPs are updated more frequently or amended with non-exempt projects. In addition, certain SIP actions relating to MVEBs may also require an updated conformity determination within 24 months. Also, conformity must be demonstrated within 12 months of EPA’s designation of an area as nonattainment for any transportation-related criteria pollutant. Project-level conformity must be determined prior to the first time a non-exempt Federal project is adopted, accepted, approved, or funded.